FIG. 1 shows one known combustor system 10 of a turbine engine. The combustor 10 includes a head-end 12, a transition 14, and a liner 16 extending therebetween. The term “combustor head-end” generally refers to the fuel injection/fuel-air premixing portion of the combustor 10. The specific components and geometry in the area of the head-end 12 can vary from combustor to combustor. The liner 16 extends from the combustor head-end 12 and toward the transition 14. The liner 16 can connect between the combustor head-end 12 and the transition 14 in any of a number of ways, as is known in the art.
The liner 16 requires cooling because of the high temperatures of the combustion occurring inside of the liner. At least a portion of the liner can be cooled by air. One known scheme for air-cooling the liner 16 includes providing a flow sleeve 18 to duct air over the hot sections of the liner 16. In one current engine design, a flow sleeve 18 is secured at one end to the head-end 12 of the combustor 10, such as the combustor casing 20. A substantially annular passage 22 can be formed between the flow sleeve 18 and the combustor liner 16, which can be substantially concentric with each other. Air 26 from the compressor section (not shown) can enter the combustor head-end 12 through the annular passage 22.
As the air travels through the passage 22, it is directed along the surface of the combustor liner 12 to provide cooling. However, in some instances, such as when a combustor has long flames, only a relatively small portion of the liner 12 needs to be cooled. Thus, a substantial portion of the air 26 is being used to cool portions of the liner 12 that are not in need of cooling. One consequence of such unnecessary cooling is an increase in system pressure drop, which in turn lowers the efficiency and power of the turbine.
Experience has revealed another problem presented by existing flow sleeves 16. In particular, the use of a flow sleeve 18 tends to increase the non-uniformity of the air flow into the combustor head-end 12. For one engine, it was discovered that the air flow into the head-end 12 is heavily skewed to the outboard radial side (with respect to the direction of the flow through the flow sleeve) whereas other areas experienced little or no flow. These uneven flow distributions can diminish the cooling effectiveness of the flow. In addition, such flow imbalances can lead to a decrease in combustor performance including the production of undesired nitrides of oxygen (NOx).
Thus, there is a need for a flow sleeve that can adequately cool the combustor liner while minimizing the system pressure drop, provide more uniform flow into the combustor, and minimize losses in engine efficiency and power.